The present invention relates to an exhaust purifier for diesel engines adapted to suppress particularly the generation of nitrogen oxides in the exhaust gas.
As for a conventional exhaust purifier for diesel engines, a technique in which water and emulsifier are added to fuel and supplied to a combustion chamber as emulsified fuel to lower the highest combustion temperature in the combustion chamber whereby generation of nitrogen oxides are suppressed is known from the description in Japanese Laid-Open Patent Application (Kokai) (A) No. Heisei 7-166962 (1995) titled “ENGINE EMULSIFIED FUEL FEEDER UNIT” and Japanese Laid-Open Patent Application (Kokai) (A) No. Heisei 7-166963 (1995) titled “ENGINE EMULSIFIED FUEL FEEDER UNIT.”
In the above official gazettes, it is surely described that the ratio of adding water (water ratio) to the fuel is decided depending on the state of load on the engine. However, they do not give any particular description about the above-mentioned water ratio, which is the most indispensable to make the technique practicable in the case of vehicles equipped with an engine that is operated in a broad load range corresponding to the running conditions, unlike the case of ships where the technique has already been put into practical use.
According to research and the experiment of the inventors, it was found that engine power performance and exhaust emission purification efficiency cannot be optimally reconciled in a broad engine operational range by fixing the water ratio to the load at a specific level or by simply increasing the water ratio in a proportional manner corresponding to the increase of the load.
The object of the present invention is to solve the above described problem and to provide an exhaust purifier for diesel engines capable of achieving better power performance and exhaust emission purification efficiency in a compatible and enhanced manner even in a broad engine operational range.